This invention relates to an apparatus for producing a picture tube which apparatus accurately measures and sets the position of an electron gun to the phosphor screen of a picture tube and seals the electron gun at a predetermined position.
In the usual production process of color picture tubes, a stem having an electron gun mounted thereto is sealed to the open end of a neck portion of a glass bulb after the phosphor screen, a graphite electrode, and the like, are formed inside the glass bulb and a shadow mask is fitted. In this case, it is necessary to bring the direction of the horizontal axis on the phosphor screen into conformity with the horizontal axis of an aperture center of an in-line type electron gun.
The production method of the type described above is carried out in the following way. As can be seen from FIGS. 8a and 8b which are plan views showing the relation of position between the glass bulb and the electron gun, the phosphor screen 1b and a graphite electrode (not shown) are formed on the inner surface of a panel 1a of the glass bulb 1 and a shadow mask or the like is fitted to the glass bulb 1. Then, the outer periphery of the panel 1a of the glass bulb 1 is brought into contact with panel stoppers 3a, 3b, 3c of a later-appearing bulb holder, not shown, as the reference, and the rotation angle .theta. between the standard axis X.sub.1 -X.sub.2 in the horizontal direction of the phosphor screen 1b determined from the panel stoppers 3a, 3b, 3c and the horizontal direction of the in-line gun M.sub.1 -M.sub.2 of the aperture centers 10.sub.1, 10.sub.2, 10.sub.3 corresponding to the blue (B), green (G) and red (R) of the electron gun disposed in such a manner as to face the phosphor screen 1b is detected. Thereafter, the electron gun is sealed into the glass bulb after the rotation angle .theta. described above is adjusted to substantially zero. Such a method is disclosed, for example, in Japanese Patent Laid-Open No. 97368/1976.
In accordance with the production method described above, the standard axis X.sub.1 -X.sub.2 of the phosphor screen 1b in the horizontal direction is detected using the outer periphery of the glass panel 1a as the reference. Since the dimension of the outer surface of this glass panel 1.sub.a has certain allowance for the material and production, the rotation angle .theta. is up to about .+-.0.5.degree.. On the other hand, color picture tubes (CRTs) ,color display tubes (CDTs) and particularly high resolution CDTs of the recent types require a severer rotation angle .theta. of within .+-.0.3.degree., for example, but it is not easy to satisfy such a requirement. Relatively large misconvergence always occurs on both ends of the picture screen and invites the drop of the picture quality. In addition, the number of steps for adjustment becomes greater and productivity drops as much.